Curvas de aprendizaje

Deciduous trees, male and female catkins are borne on bare wood in late winter and early spring. In general, they are medium to large and used as street trees and parkland trees and in native and naturalistic schemes (Table 4.4). Trees from the Betulaceae are cultivated for functional and ornamental uses.

TYPES OF PLANTS.Medium–large trees, Alnus, Betula, Carpinus and Corylus.

Table 4.3. Sequence of flower of Mahonia from November/December to April/May.

Mahonia lomariifolia: with tall architectural habit and pinnate dark green leaves. Yellow flowers in upright racemes 20–30 cm long

Mahonia ‘Charity’: foliage not as long as M. lomariifolia, with tall upright racemes, yellow flower. A hybrid of Mahonia japonica× M. lomariifolia, with the habit of the shrub more inclined to the latter.

Mahonia japonica: wide-spreading racemes of yellow flowers.

Mahonia aquifolium: short stumpy racemes of yellow flowers with pinnate leaves and good bushy habit, useful for ground cover

WORLD DISTRIBUTION. North temperate regions, some species occur in North America, USA and Canada, others in China and in Europe. Alnus, Corylus and Betula are native in Western Europe.

LEAVES. Deciduous leaves are alternate, simple, entire, some with serrated margins. The leaf veins are generally prominent.

Alnus leaves are often shiny and broad. Winter buds are stalked, a distinguishing feature from the other genera in the family (Fig. 4.3).

Betula leaves are often triangular in outline and thin in texture. Winter buds are small.

Carpinus leaves are oblong-ovate in shape, with 15 pairs of parallel-ribbed leaves. Winter buds are sharp-pointed with overlapping scales.

Corylus leaves are round in outline, often hairy to the touch. Winter buds are ovoid.

Table 4.4. Trees from the Betulaceae cultivated for functional and ornamental uses.

Species Common name Functional use Ornamental use Size (m)

Betula albosinensis Parkland tree Red/plum-stemmed 20

var. septentrionalis specimen tree

Betula ermannii White-stemmed 20

specimen tree

Betula pendula Weeping birch Mass planting, White-stemmed 20–30 reclamation sites specimen tree

B. pendula ‘Youngii’ Weeping specimen 5–8

tree

Betula pubescens Downy birch Mass planting, 10–20

reclamation sites

Betula utilis Himalayan birch Landscape tree White-stemmed 15 specimen tree

B. utilis var. Himalayan birch Landscape tree White-stemmed 12–15

jacquemontii specimen tree

Alnus cordata Italian alder Landscape tree Glossy green foliage 25

Alnus glutinosa Alder Mass planting, 20

reclamation sites

Alnus incana Grey alder Mass planting, 25

reclamation sites

A. incana ‘Aurea’ Specimen tree 5–8

A. incana ‘Laciniata’ Specimen tree 8–10

Carpinus betulus Hornbeam Parkland tree, hedge 25–30

C. betulus ‘Fastigiata’ Street tree 20–25

Corylus avellana Hazel 10–12

C. avellana ‘Aurea’ Specimen tree with 5–8

yellow foliage

C. avellana ‘Contorta’ Contorted hazel Specimen shrub, 2–3 a curiosity

Corylus colurna Turkish hazel Street tree 20

Corylus maxima Specimen tree with 8–10

‘Purpurea’ purple foliage

FLOWERS. Unisexual flowers are borne in early spring before the leaves emerge. Male flowers are held in erect or pendulous catkins and female flowers in erect catkins.

FRUIT. A small or large nut, sometimes conspicuous, sometimes not, occurs in these trees.

Alnus fruit are green woody ‘cones’, turning brown as winter progresses and held on the tree for several months and occasionally to the following season.

Betula fruit are very tiny but the overall catkin can be several centimetres long. Seed is shed over the winter months and the catkin disintegrates on the tree.

Corylus fruit is the common hazelnut, with two nuts fused together and enveloped within a leaf-like involucre.

Carpinus fruit are tiny nutlets held in a pendulous catkin, each nutlet enveloped in a green leafy bract.

BARK.The bark is white in several species of Betula (birch), making them important trees for winter interest in amenity planting schemes. Shaggy peeling bark occurs in Betula nigra (river birch). A thick cork-like bark is a feature of Corylus colurna (Turkish hazel).

GROWTH RATE AND LONGEVITY. They are fast-growing and generally short-lived, 40–50 years.

FUNCTIONAL AND ORNAMENTAL USES.

Parkland trees Betula pendula and B. pendula

‘Dalecarlica’, Carpinus betulus Street trees C. betulus ‘Fastigiata’, B. pendula

and Corylus colurna

Specimen trees for winter interest Betula utilis var. jacquemontii and B. ermanii

Native/naturalistic planting schemes Corylus avellana, B. pendula, B. pubescens and Alnus glutinosa

Damp sites, soil stabilization and Alnus incana and B. pendula reclamation sites

Specimen trees for autumn colour B. pendula Fig. 4.3. (A) Alnus cordata, Italian alder; (B)

Alnus glutinosa, common alder; (C) Alnus incana, grey alder; (D) Alnus rubra, red or Oregon alder. (From Savill, 1991.)

Garden trees Some particular forms of Alnus have been selected: A. incana ‘Aurea’, with yellow leaves and orange-coloured young shoots and catkins, and A. incana ‘Laciniata’, with dainty cut-leaved foliage.

Hedges Carpinus betulus

GROWING CONDITIONS. Alnus thrive in moist soils. They can fix atmospheric nitrogen.

B. pendula is an early colonizer of bare ground and requires plenty of light. It grows in poor sandy soils.

B. pubescens and B. nigra are suited to damp soils.

MANAGEMENT.See the section in Chapter 5, Trees: Selection, Use and Management.

PESTS AND DISEASES.In Betula, distorted growth forming a witches’ broom is caused by Phytoptus rudis, an insect.

PARTICULAR PLANTING SCHEMES OR PLANT ASSOCIATIONS. At Mount Usher, Couny Wicklow, Ireland, a specimen tree Betula maximowicziana of some 20 m tall is well positioned by a pond with a backdrop of taller trees.

Native woodland of B. pendula occurs in many parts of Ireland and Scotland.

Corylus avellana (hazel) clothes some of the extensive limestone pavement of the Burren, County Clare, Ireland.

Extensive hedges of Carpinus betulus (hornbeam), known as charmilles, form part of the baroque gardens in Versailles and Vaux-le-Vicomte, France, Sans Souci, Potsdam, Germany, and Belvedere and Schönbrunn, Vienna, Austria.

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